The present invention relates to a device for preventing the scorching of a hot-gas-wetted metal wall of a gas turbine engine or the like which is energized with cooling air and has cooling air holes communicating with intermediate spaces formed between a thin metal skin lining and the metal wall.
Combustion chambers of modern gas turbine engines, e.g., come under extremely high thermal loads, for the reason that high engine efficiency requires high combustion chamber exit or turbine inlet temperatures. In order to minimize the cooling effort for the combustion chamber wall, a clamshell construction as exemplified in DE-OS 34 24 345 has been selected that consists of a load-bearing structure (metallic outer shell) and an internal covering structure (e.g. shingle-shaped metallic or ceramic liner). Then when damage caused, e.g., by local overheating or material degradation or the like causes a metal shingle to partly fuse or a portion of a ceramic shingle to break off, the little-cooled metallic outer shell of the combustion chamber is directly exposed to the attack of hot combustion gases. This may cause the outer shell to scorch.
In order to mitigate the risk of the combustion chamber outer wall to overheat or scorch, it has already been proposed to provide the inner side of this component with a radiation-reflective layer in, e.g., silver or platinum (vapor plated).
It has also been proposed in connection with stationary gas turbine engines to fill the space between the outer wall of the combustion chamber and the inner liner with ceramic insulation and a metallic, resilient filler material.
In this manner and with this construction of the combustion chamber, however, the risk of scorching of the metallic outer wall in the train of damage or rupture of the inner shingle structure of the combustion chamber, could not be fully combatted, either.
In a broad aspect of the present invention a device of the initially cited generic category is provided for optimal overheat protection for the metallic structural component at relatively little cooling effort; this will largely minimize the risk of scorching the respective metallic structure as a result of damage to the liner structure that normally shields from the hot gases or combustion gases.
It is a particular object of the present invention to provide a device wherein the metal wall is shielded from the hot gas flow by at least one highly temperature resistant wall element, which together with the metal skin, includes at least one cavity, with the thin metal skin being of a material which is locally ruptured by hot gases upon the failure of the highly temperature resistant wall element thereby exposing the cooling air holes to the hot gas flow.
The present invention finds advantageous use not only with combustion chambers of gas turbine engines, but can be used wherever metallic outer component structures, such as casing component structures in the radially spaced-apart vicinity of other liners, are exposed to extremely high temperatures from hot gases as, e.g., with turbine rotor blade shells which are conventionally cooled with air taken from the compressor exit (impingement cooling systems), where the shell section immediately adjacent to the rotor blade tips is exposed to extremely high temperature effects.
The invention is suitable also for use in afterburners of gas turbine engines, in which extremely high combustion temperatures occur, so that also in this environment the metallic outer tail pipe structure can be lined with an internal shingle- or scale-like liner.
The invention can be used to advantage also with cooled stator vanes or rotor blades of gas turbine engines, i.e. with blade concepts, in which the cooling air is blown from one or several internal blade cavities and through one or several rows of impingement cooling holes in a metallic inner wall against highly temperature-jeopardized wall sections of the outer blade shell, where said extremely highly temperature-jeopardized blade shell sections are represented especially by the blade leading and trailing edge portions.
When referred to, e.g., the combustion chamber of a gas turbine engine the object of the present invention is advantageously represented in design and effect as follows: The outer load-bearing structure of the combustion chamber consists of a metallic outer shell provided with a plurality of small radial holes of one or several internal sheet metal components of thin section. The thin metal skin is locally positively connected to the load-bearing structure, but is in wide areas radially spaced apart from the outer shell.
The thin metal skin prevents the admission of air into the combustion chamber through the many small radial holes. In accordance with the present invention the melting point of the metal skin material is equal to or lower than that of the outer shell. Then when a metal or ceramic shingle is damaged, the hot combustion gases first impinge on the thin-walled metal skin. This area of the metal skin overheats and melts. This exposes a number of radial holes in the outer shell. The compressor air flows through these holes and into the combustion chamber, intensively cooling the load-bearing structure in the vicinity of the damaged shingle and simultaneously keeping the hot combustion gases away from the outer shell. At the next inspection of the combustion chamber the defective shingle and/or a portion of the metal skin will be replaced.